POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: South Korean Marine's Landing Vehicle Tracked (LVT) move their position during the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: South Korean Marine's Landing Vehicle Tracked (LVT) move their position during the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan, and South Korean marines participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan, and South Korean marines participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan, and South Korean marines participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: South Korean marine's Landing Vehicle Tracked (LVT) move their position during the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: South Korean Marine's Landing Vehicle Tracked (LVT) move their position during the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: South Korean Marines participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan, and South Korean marines participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

POHANG, SOUTH KOREA - MARCH 31: U.S. Marines from 3rd Marine Expeditionary Force, Battalion landing team deployed from Okinawa, Japan participate in the U.S. and South Korean Marines joint landing operation at Pohang seashore on March 31, 2014 in Pohang, South Korea. It has been reported by South Korean media that the scale of this annual joint exercise is one of the largest in the past. (Photo by Chung Sung-Jun/Getty Images) Chung Sung-Jun Getty Images

PERTH, AUSTRALIA - MARCH 31: Members of South Korea's (L) and China's defense forces take pictures of Australian Prime Minister Tony Abbott (not pictured) as he addresses them during his visit to RAAF Base Pearce on March 31, 2014 in Perth, Australia. The search continues off the Western Australian coast for Malaysia Airlines flight MH370 that vanished on March 8 with 239 passengers and crew on board. The flight is suspected to have crashed into the southern Indian Ocean with no survivors. (Photo by Jason Reed-Pool/Getty Images) Pool Getty Images

South Korean Marine amphibious assault vehicles land on the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marine amphibious assault vehicles land on the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marine amphibious assault vehicles land on the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US (L) and South Korean (bottom) marines take a positon during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marine amphibious assault vehicles land on the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines take a positon during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines take a positon during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines sit in an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines get out from an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines get out from an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean (R) and US (L) Marines gesture to a point during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines take a position during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a "new form" of nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines take a position as South Korean policemen stand guard to block protestors during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North and South Korea traded fire across their disputed maritime border on March 31, with the South's military saying it had responded to shells landing in its waters from a North live-fire drill. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean anti-war activists march near a beach as policemen stand guard during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North and South Korea traded fire across their disputed maritime border on March 31, with the South's military saying it had responded to shells landing in its waters from a North live-fire drill. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean anti-war activists march near an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North and South Korea traded fire across their disputed maritime border on March 31, with the South's military saying it had responded to shells landing in its waters from a North live-fire drill. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

US Marines take a position during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North and South Korea traded fire across their disputed maritime border on March 31, with the South's military saying it had responded to shells landing in its waters from a North live-fire drill. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

A US Marine takes a position during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North and South Korea traded fire across their disputed maritime border on March 31, with the South's military saying it had responded to shells landing in its waters from a North live-fire drill. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

A South Korean Marine sits in an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marines stand on a beach as amphibious assault vehicles (in background) head toward the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marines take a position on a beach during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

A South Korean Marine stands on a beach as amphibious assault vehicles (in background) approach the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marines exit an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

A South Korean Marine (C) gives directions during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images

South Korean Marines exit an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. Meanwhile, the two Koreas traded hundreds of rounds of live artillery fire across their disputed maritime border, forcing South Korean islanders to take shelter a day after the North drove up tensions by threatening a new nuclear test. AFP PHOTO / JUNG YEON-JE (Photo credit should read JUNG YEON-JE/AFP/Getty Images) JUNG YEON-JE AFP/Getty Images